Adhesion among chick embryo nerve cells requires the function of a cell surface polypeptide called CAM. Specific antibodies against CAM inhibit neural cell aggregation, the fasciculation of neurites, sorting out of retinal cells in aggregates, and also perturb the formation of cell and neurite layers in cultured retinal tissue. CAM-mediated adhesion has also been shown to influence the NGF-induced growth, attraction and retraction of nerve fibers. Recent studies indicate that adhesion among embryonic liver cells occurs by a different mechanism involving another cell surface protein that is antigenically distinct from CAM. During the next year our research will include a detailed chemical characterization of CAM, including structural comparisons to the liver cell adhesion molecule, as well as experiments on the precise function of CAM in the mechanism of cell-cell binding. These studies should contribute to a fundamental understanding of how cell-cell interactions affect tissue formation during embryogenesis.